1. Field of the Invention
The invention described herein relates to word processors and particularly to new and improved means for recording tab functions.
2. Description of the Prior Art
A word processor system generally comprises a data storage unit such as a magnetic recording medium or semiconductor memory and a typewriter serving as an input/output device to permit communication between the typewriter and storage unit. The system may be operated as a conventional typewriter or in various other modes, for instance, RECORD, PLAY, INSERT, DELETE and SKIP. In the RECORD mode, typed data may be printed on paper as in the case of conventional typewriter operation and simultaneously recorded in the data storage unit in the form of coded signals representative of the respective characters. In the INSERT and DELETE modes, new coded data signals may be inserted and original coded data signals deleted, respectively, at selected points in previously recorded data; and by means of the SKIP mode fast access may be obtained to the selected points for making the insertions and deletions. In the PLAY mode, the signals recorded in the data storage unit act to control the typewriter to print out the recorded data. The printout or playback is made in response to operator actuation of appropriate typewriter action keys, for example, CHARACTER, WORD, LINE and AUTO which function respectively to produce the playback on an individual character, word, line or block basis.
Other modes and actions in addition to those mentioned above are employed in various word processor systems as is well known in those skilled in the art. Moreover, the performance capabilities, uses and interrelationship of the various modes and actions are also well understood by those skilled in the art and thus for ease of explanation and understanding, the improvement afforded by the present invention will be explained only with reference to the RECORD and PLAY modes.
Typically, in the RECORD mode of operation the respective characters and format functions such as tab, space, backspace and carrier return are represented by unique digital encoded signals which are recorded in the data storage unit. In the case of a single element typewriter, for example, where the type characters are on a ball shaped member which moves along the typing line on a carrier mechanism and tilts and rotates in appropriate manner to print the various characters, an eight bit digital signal can represent each character or format action. A space function, for instance, may be represented by all zeros. For characters, two bits and four bits respectively can represent the tilt and rotation positions of the type element while a seventh bit indicates capital or lower case and the eighth bit indicates whether the type is to be underlined. Other unique eight bit signals can be used to represent format actions such as tab, backspace and carrier return.
An operator tab command, which causes the typewriter carrier mechanism to move rapidly to the right from its instant position to the next tab stop, is customarily recorded in presently available word processors as a unique digital signal which functions subsequently during playback to cause a tabbing action of the typewriter carrier mechanism. Recording in this manner does not assure preservation of text format on playback. If the typewriter tab stops are located at the same position for both recording and playback and no insertions or deletions are made in the storage unit at a point preceding a recorded tab command signal, the playback text format will indeed be the same as that which was recorded. On the other hand, if the tab stop locations are different during playback from those used during recording, the text format will not be preserved, that is, playback format will be different from what was recorded. Moreover, even if the tab stops are the same, the text format will not be preserved if the location of recorded tab command signals in the data storage unit as been materially altered by insertions or deletions. In any case, the change in text format occurs for the simple reason that tab command is recorded as an encoded tab function signal which provides a predetermined tab instruction to the typewriter during playback, independent of and without any regard to the instant position of the carrier or present location of tab stops.